Integrated temperature controlled exhaust and cold trap assembly

ABSTRACT

A temperature-controlled exhaust assembly with cold trap capability. One embodiment of the exhaust assembly comprises a multi-heater design which allows for independent multi-zone closed-loop temperature control. Another embodiment comprises a compact multi-valve uni-body design incorporating a single heater for simplified closed-loop temperature control. The cold trap incorporates a heater for temperature control at the inlet of the trap to minimize undesirable deposits. One embodiment also comprises a multi-stage cold trap and a particle trap. As a removable unit, this cold trap provides additional safety in the handling and disposal of the adsorbed condensables.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application contains subject matter that is related tocommonly-assigned U.S. patent application Ser. No. 09/211,998, entitled“High Temperature Chemical Vapor Deposition Chamber”, filed on Dec. 14,1998, which is herein incorporated by reference.

BACKGROUND OF THE DISCLOSURE

[0002] 1. Field of the Invention

[0003] The invention relates to a temperature controlled exhaustassembly for a semiconductor wafer processing system and, moreparticularly, to an integrated exhaust assembly having temperaturecontrol with cold trap capability.

[0004] 2. Description of the Background Art

[0005] In the development of wafer processing equipment for devicemanufacture, the design of an exhaust system may be as important as thatfor the process chamber. Many, if not most, of the processes used insemiconductor device fabrication involve either corrosive or toxicchemical precursors. Very often, the process reactions lead to similarlytoxic by-products, or leave undesirable deposits on interior surfaces ofthe chamber and/or exhaust assembly. Therefore, the design of an exhaustsystem should address environmental concerns and safety considerationsfor operating personnel, as well as the need for ease of maintenance ofsystem components.

[0006] Different types of traps are commercially available for use in anexhaust line to trap a variety of chemicals. Examples include molecularsieve traps which work by chemisorption and cold temperature traps fortrapping condensable materials. Off-the-shelf cold traps typicallyinvolve only a single stage design, and may not have sufficient trappingefficiency to meet certain processing demands. One example of a processthat exceeds the capabilities of existing cold traps is the depositionof titanium nitride (TiN) film from a reaction between titaniumtetrachloride (TiCl₄) and ammonia (NH₃). In addition to the reactionproducts titanium nitride (TiN), nitrogen (N₂) and hydrogen chloride(HCl), other by-products such as adduct ammonia salts are formed. It isfound that existing single-stage cold traps cannot effectively trapreaction by-products under certain operating and pumping conditions,resulting in the need for additional design remedies.

[0007] Another level of complexity also arises because the nature of thematerial deposit from the TiCl₄/NH₃ reaction is temperature dependent.Therefore, TiN film deposition is often performed at a temperature ofpreferably above 600° C. In designing a TiN deposition chamber using ahigh temperature reaction, it is also desirable to maintain the exteriorchamber walls at a lower temperature to ensure the safety of operatingpersonnel. Such a high temperature chemical vapor deposition chamber forTiN film deposition is described in a commonly-assigned U.S. patentapplication Ser. No. 09/211,998, entitled “High Temperature ChemicalVapor Deposition Chamber”, filed on Dec. 14, 1998, and is hereinincorporated by reference. This high temperature chamber comprises aheated liner which is thermally isolated from the chamber body such thatthe chamber exterior remains at a temperature of about 60° C. Since TiNfilm or reaction by-products are also deposited on the interior surfacesof the chamber, periodic chamber cleaning is needed to maintain reliableprocess performance. It is known in the art that for the TiCl₄/NH₃ basedchemistry, a small amount of TiN film is formed at a temperature between150° C. to 250° C. This film can readily be removed by a chlorine-basedchamber cleaning process. Below 150° C., however, an adduct salt powderdeposit is formed, but it is resistant to the chlorine-based cleaningprocess. It is thus highly desirable to maintain the interior walls ofthe chamber and exhaust assembly at a temperature between 150° C. to250° C. to facilitate routine chamber cleaning and system maintenance.

[0008] Therefore, a need exists in the art for a temperature controlledexhaust system.

SUMMARY OF THE INVENTION

[0009] The present invention is a temperature-controlled exhaustassembly with cold trap capability, which can be used in conjunctionwith a variety of process chambers for different semiconductor waferprocessing applications. Specifically, the inventive exhaust assemblycontains a conduit for exhaust gases that has at least one attachedheater and temperature sensor, and a cold trap connected to the conduit.By maintaining the temperature of the conduit within a range appropriatefor the specific process, deposit formation on the interior walls of theconduit can be controlled to reduce the frequency of routine chambermaintenance. A water-cooled cold trap is also provided to adsorb anycondensables from the exhaust gases prior to an exhaust pumping system.The present invention has been used in conjunction with a hightemperature chemical vapor deposition chamber for TiN film depositionusing a TICl₄/NH₃ chemistry. Since the nature and property of thedeposit from this reaction is temperature dependent, it is important tocarefully control the chamber temperature in order to achieve optimalprocess and chamber performance. For example, chamber maintenance isgreatly facilitated by maintaining the exhaust assembly within atemperature range of about 150-250° C., because the TiN deposit formedon the interior surfaces of the exhaust assembly can readily be removedby a chlorine-based chamber cleaning process. A cold trap is alsoprovided to adsorb condensables, such as hydrogen chloride (HCl), orother reaction by-products from the exhaust gases.

[0010] One embodiment of the invention comprises a multi-heater design,which incorporates a total of six external heaters to heat differentportions of the exhaust assembly. Each heater also has an associatedtemperature sensor to allow for independent closed-loop feedback controlby a controller. Furthermore, this embodiment incorporates a singlestage multi-loop coil cold trap as an integral component of the exhaustassembly. The cold trap comprises a single baffle plate located close tothe entrance of the trap, and a multi-loop cooling coil carrying coolingwater at a temperature of about 20°-25° C. Condensables from the exhaustgases are adsorbed onto surfaces of the baffle plate and coil. When usedin conjunction with the TiN deposition chamber using TiCl₄/NH₃chemistry, the entire exhaust assembly is maintained within the sametemperature range of 150°-200° C. While this particular application doesnot take full advantage of the multi-heater design by using a variety oftemperatures, it is recognized that this embodiment can potentiallyprovide process control flexibility through independent multi-zonetemperature control.

[0011] Another embodiment comprises a compact integrated multi-valveuni-body assembly with a single heater that controls the temperature ofthe assembly. Several valves are mounted onto a single aluminum bodywhich also accommodates a thermoelectric heater and a temperaturesensor. For applications requiring temperature control within a singlerange, this single-heater design greatly simplifies the closed-looptemperature control operation. The unique compact multi-valve uni-bodydesign allows for easy control within a temperature range of about150-200° C. when used in conjunction with the high temperature TiNdeposition chamber.

[0012] The valve body also provides vacuum ports for adapting to aremovable multi-stage trap assembly, which incorporates a multi-stagecold trap and a particle trap. The cold trap provides multi-stageadsorption through a series of cold baffle plates. The baffle platescontain an arrangement of apertures that are offset from each other. Assuch, the probability of collisions between gas molecules and the baffleplate surfaces is increased, leading to significant improvement intrapping efficiency for condensables such as HCl, or other reactionby-products.

[0013] This embodiment provides added operational flexibility becausethe multi-stage trap can readily be isolated and removed from the restof the exhaust assembly. By closing two compact shut-off valves providedrespectively at the inlet and outlet of the trap, the adsorbedcondensables can be safely contained within the trap and transported toother locations for proper disposal. With its flexible temperaturecontrol and compact design, the exhaust and trap assembly can readily beretrofitted and adapted for use with any vacuum chamber for a variety ofprocess applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The teachings of the present invention can be readily understoodby considering the following detailed description in conjunction withthe accompanying drawings, in which:

[0015]FIG. 1a depicts a cross-sectional view of a first embodiment of aclosed-loop temperature controlled exhaust and cold trap assembly;

[0016]FIG. 1b depicts a schematic diagram for closed-loop temperaturecontrol;

[0017]FIG. 2 depicts a perspective view of a second embodiment of thepresent invention, comprising an integrated temperature controlledexhaust and a multi-stage cold trap;

[0018]FIG. 3a is an exploded perspective view of the multi-stage coldtrap shown in FIG. 2;

[0019]FIG. 3b is a side view of the multi-stage cold trap shown in FIG.2;

[0020]FIG. 4a is a front view of the first vertical baffle plate shownin FIG. 3b;

[0021]FIG. 4b is a front view of the second vertical baffle plate shownin FIG. 3b;

[0022]FIG. 5a is a top view of the first horizontal baffle plate shownin FIG. 3b;

[0023]FIG. 5b is a top view of the second horizontal baffle plate shownin FIG. 3b;

[0024]FIG. 5c is a top view of the bottom filter plate of the shown inFIG. 3b;

[0025]FIG. 6 is a cross-sectional view of an alternative arrangement ofbaffle plates inside a multi-stage trap; and

[0026]FIG. 7a is an exploded view of the shut-off valve for use with themulti-stage cold trap of FIG. 3b; and

[0027]FIG. 7b is a cross-sectional view of the assembled shut-off valveshown in FIG. 7a.

[0028] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon to the figures.

DETAILED DESCRIPTION

[0029] Exhaust Assembly with Multi-Zone Heating

[0030]FIG. 1a depicts a cross-sectional view of one embodiment of atemperature controlled exhaust assembly 100 and its associated vacuumadapting components 110 that are used to connect it to a process chamber(not shown). These vacuum adapting components 110 comprise: an adapterplate 101, a thermal insulator 102, an exhaust tubing (conduit) 103, aband heater 105, a cover plate 104, a 20-torr Baratron 106, and areducer 107. The annular adapter plate 101 mates directly to a sideopening 192 of the process chamber (not shown), and fits around theoutside of an exhaust tubing 103 which extends partly into the sideopening 192. A thermal insulator 102 is fitted adjacent to the adapter101 on the side away from the process chamber exterior wall 191. Thisthermal insulator 102 provides insulation between the heated exhaustassembly 100, which is maintained at a temperature of, for example,about 150° C., and the process chamber exterior wall 191, which ismaintained at a temperature of about 60-65° C. A stainless steel bandheater 105 circumscribes a substantial portion of the outside wall ofthe exhaust tubing 103. An annular cover plate 104 fits over the outsideof the insulator 102, the band heater 105 and the remaining exhausttubing 103. In an alternative embodiment, a single flexible heater (notshown) may also be used to heat both the exhaust tubing 103 and thereducer 107. An insulating jacket 109 made of silicone material fitsover the annular cover plate 104 and the reducer 107 to prevent possibleinjury to operating personnel. The reducer 107 connects, at its largerdiameter opening 117, to the far end 113 (away from the process chamber)of the exhaust tubing 103, and at its smaller diameter opening 127, toadditional components of the exhaust assembly 100. A 20-torr Baratronpressure gauge 106 is connected through the side wall of the reducer 107to monitor the pressure within the exhaust assembly 100.

[0031] In this embodiment, the exhaust assembly 100 also comprises acold trap 150, in addition to several vacuum valves 120, 140, 160 and170 for controlling the pumping operation. As such, the various vacuumcomponents (e.g., exhaust tubing 103, reducer 107, cold trap 150, andvacuum valves 120, 160, 170) collectively define a passage way, orconduit, for the exhaust gases within the exhaust assembly 100.Multi-zone temperature control of the exhaust assembly 100 is providedby numerous heaters at various locations of the exhaust assembly 100.These flexible heaters are made of silicone materials, and are wrappedaround the exterior walls of the exhaust assembly 100 underneath theirrespective insulating fabric jackets—these heater/jacket combinationsare designated as 125, 145, 155, 165, 175 in FIG. 1a. Thermocoupletemperature sensors (not shown in FIG. 1a) are also provided with theseheaters, and may be used for closed-loop feedback control of the heatertemperature via a control console 199 (see FIG. 1b) comprising acontroller 193.

[0032]FIG. 1b depicts schematically the control console 199 connected toa series of temperature sensors 197 ₁, 197 ₂, . . . , 197 ₅(collectively sensors 197 _(i)) and the associated heaters 198 ₁, 198 ₂,. . . , 198 ₅ (collectively heater 198 _(i)). In this particularembodiment, each heater 198 _(i) is also connected to a power supply 195via a thermostatic switch 196 _(i). The heaters 198 _(i) and temperaturesensors 197 _(i), for example, are disposed around the various valvesand vacuum components of the exhaust assembly 100 as discussed below. Asshown in FIG. 1b, all the heaters 198 _(i) are maintained at the sametemperature setting by connecting them in series to the control console199. The control console 199 comprises, for example, a Watlow 965 PIDcontroller 193 and several adjustable temperature interlocks 194. Forthe current TiN chamber application, a single point temperature controlfor the entire exhaust assembly 100 is found to be adequate. Forexample, effective closed-loop temperature control is achieved bymonitoring the temperature sensor 197 ₂ located around the manual valve120. As a safety precaution, other sensors 197 ₁, 197 ₃, 197 ₄ and 197 ₅are provided with heaters 198 ₁, 198 ₂, 198 ₄ and 198 ₅ (correspondingto heaters 105, 125, 155 and 165 in FIG. 1a) and are used in conjunctionwith the temperature interlocks 194 for “over temperature” control. Thedesign flexibility in the present invention is further illustrated inthe embodiment shown in FIG. 1b, where over-temperature protection forthe heaters 198 ₂ (corresponding to heater 125 for the valve 120) and198 ₃ (corresponding to heater 145 for the valve 140) are effectivelyprovided by a single sensor 197 ₃. Such “shared” protection is possibledue to the proximity of the heaters 125 and 145 to one another. Bymodifying connections to the control console 199, the heaters 198 canalso be individually connected to additional power supplies 195 (notshown) to allow for independent temperature control at differenttemperature settings. The heaters, temperature sensors and controlconsole 199 are customized for the current application and are availableas Applied Materials part number 1410-01304, or Nor-Cal part numberNC-000001-2.

[0033] When used in conjunction with the high temperature TiN depositionchamber using TiCl₄/NH₃ chemistry, the exhaust assembly 100, with theexception of the cold trap 150, is maintained at a temperature ofapproximately 150-200° C. so as to reduce undesirable deposits fromcoating the interior of the exhaust assembly 100. This embodiment isespecially well suited to other applications which may require separatetemperature control for different parts of the exhaust assembly 100. Forexample, a heater 125 (such as 198 ₂ in FIG. 1b) is used to heat anangle valve 120, which serves as an inlet valve for the exhaust assembly100. The angle valve 120 is provided with three vacuum ports, 121, 122and 123. The valve 120 is connected to a process chamber (not shown) viathe reducer 107 at the inlet port 121, and is connected at the outletport 122 to a cold trap 150, which is provided with its own heater 155,e.g., 198 ₄ of FIG. 1b. With suitable modifications, the angle valve 120and the cold trap 150 can be independently temperature-controlled, ifdesired.

[0034] The vacuum port 123 at the side of the angle valve 120 isconnected to the port 141 of a manual valve 140. The manual valve 140,which is fitted with a separate heater 145, such as 198 ₃ of FIG. 1b,may be used to connect, via a port 142, to other vacuum accessories orprocess diagnostic equipment such as a leak detector or a residual gasanalyzer (RGA).

[0035] The cold trap 150 is connected at its inlet 151 to the valve 120,and at its outlet 152 to an isolation valve 160. The cold trap 150houses a baffle plate 159 and a multi-loop cooling coil 156. Both thehousing 150 and the baffle plate 159 are made of stainless steel withnickel plating, although other materials are also acceptable providedthat they are chemically compatible with the process gases used. Thebaffle plate 159 is mounted close to the inlet 151 of the cold trap 150,and is suspended from the top 150T of the cold trap 150 by stainlesssteel spacers 157, which are either screwed in or brazed to the baffleplate 159. The cooling coil 156, which is suspended inside the cold trap150, is brazed to the bottom 150B of the cold trap 150. The cooling coil156 has an inlet 156 i and an outlet 156 o. A circulating heat transferfluid, such as cooling water, enters the cold trap 150 via the inlet 156i and leaves via the outlet 156 o. The multi-loop coil 156 provides alarge cold surface area for trapping condensables from the exhaustgases. For example, an inlet water temperature of about 20-25° C. may beused for trapping condensables generated from a TiCl₄/NH₃ based TiNdeposition process. Of course, other cooling media can also be used asappropriate, especially if lower temperature application is desired.Although the present embodiment uses a multi-loop coil, other designssuch as cooled metal strips or fin-like structure may also be used. Thekey point is that a larger cooled surface area is preferable in order toincrease the trapping efficiency of the cold trap.

[0036] As shown in FIG. 1a, an external heater 155 (e.g., 198 ₄ in FIG.1b) is also used for temperature control around the cold trap 150. Forexample, when used in conjunction with the high temperature TiNdeposition chamber, the external heater 155 provides heating around theinlet 151 of the trap 150. With the heater 155 adjusted for atemperature of about 150° C., and a cooling coil temperature of about20-25° C., the temperature of the baffle plate 159 can be maintainedwithin a range of 40-70° C. This design of the heater 155 and coolingcoil 156 locations leads to a temperature gradient being establishedalong the cylindrical side 150S of the cold trap 150. For example, thetop 150T of the trap 150 has a temperature of about 70° C., whichdecreases to about 45° C. at some intermediate distance, while thebottom 150B of the trap 150 has a temperature of about 30° C. The heater155 serves to minimize deposits around the inlet 151 and the baffleplate 159. Due to the lower temperature at the bottom 150B of the trap150, condensables tend to deposit there first. Therefore, thisparticular design helps minimize excessive deposit build-up towards theinlet 151 of the trap 150, which would otherwise lead to deteriorationof trapping performance.

[0037] When exhaust gases enter the cold trap 150 through the inlet 151,which is located along a center axis of the cold trap 150, they arediverted by the baffle plate 159 to flow radially outwards towards thecylindrical side 150S of the cold trap 150. Some condensables aretrapped onto the baffle plate 159, while most are trapped onto the coldsurface of the multi-loop cooling coil 156. The remaining exhaust gasesare pumped through an axially located tube-like channel 158 prior toexiting the cold trap 150 via the outlet 152.

[0038] An isolation valve 160 connects between the outlet 152 of thecold trap 150 and a throttle valve 170. This isolation valve 160 can beused to isolate the exhaust and cold trap assembly 100 from the pumpingforeline 190. The isolation valve 160 is also used, in conjunction withthe throttle valve 170, to allow for proper sequencing and pressurecontrol during the process and pump-down cycle. Furthermore, both theisolation valve 160 and the throttle valve 170 are equipped withexternal heaters 165 and 175. The heater 165, for example, correspondsto 198 ₅ shown in FIG. 1b. The heater 175 used in this embodiment isprovided with a built-in thermostat control, and is not connected to thecontrol console 199. Since the cold trap 150 is not 100% effective intrapping all condensables from the exhaust gases, heaters 165 and 175are needed in order to prevent the formation of undesirable powderdeposit inside the valves 160 and 170. Heater jackets 129, 119 a, 119 b,119 c, and 119 d are also provided around the angle valve 120 andvarious clamp areas of the exhaust assembly 100 both to minimize heatloss and to provide a safe operating environment.

[0039] Although a chlorine-based chamber cleaning process providesefficient dry cleaning of the interior of the exhaust assembly 100 aftereach wafer deposition, powder deposits tend to accumulate after anextended period of wafer processing—e.g., 5000 wafers. These depositscan readily be removed by cleaning with water or hydrogen peroxideduring periodic maintenance. The use of the heated exhaust assembly 100contributes to equipment uptime by reducing the time required forcleaning and extending the time interval between chamber cleans.

[0040] Integrated exhaust assembly

[0041] Another embodiment of the present invention comprises anintegrated uni-body exhaust assembly-200 shown in a perspective view inFIG. 2. In this embodiment, a single valve body 205 houses severalvalves 210, 220, 230, 240 and vacuum ports 212, 231 for adapting to aremovable cold trap 300. The valve body 205 is fitted with a singlecartridge heater (not shown) within recess 201 and a thermocouple sensor(not shown) within recess 202 for temperature monitor and control. Thisembodiment encompasses a unique compact design, whose size is reduced toalmost ⅓ of that of the multi-heater design illustrated in FIG. 1a. Withonly one heater and one temperature sensor, this new design offers asimplified electrical control and temperature management system forapplications requiring only a single temperature control. Additionalprocess flexibility and safety is achieved through the removablemulti-stage trap 300, which can be isolated from the valve body 205 byclosing valves 391 and 392 prior to removal of the trap 300 from theassembly 200.

[0042] Four valves 210, 220, 230, 240 are mounted on a valve body 205made from a solid block of aluminum having ports and bores for thevalves milled into the block. These valves include: 1) amanually-operated valve 210 for isolating the process chamber (notshown) from the exhaust assembly 200; 2) an angle valve 220 for couplingto other wafer processing system accessories (not shown), 3) a pneumaticvalve 230 for isolating the exhaust assembly 200 from the exhaust pumpline (not shown), and 4) a throttle valve 240 located between thepneumatic valve 230 and the exhaust pumping system (not shown) thatconnects to a vacuum tubing (conduit) 250. To ensure proper pressurecontrol and sequencing of valve operation during the process andpump-down cycle, the operation of the isolation valve 230 issynchronized with the throttle valve 240, although such synchronizedoperation is not absolutely necessary to achieve proper operation of theexhaust assembly 200. Similar to the embodiment described previously,the various components such as valves 210, 220, 230, 240, valve body205, and tubing 250, collectively define a passageway, or conduit, forexhaust gases within the exhaust assembly 200.

[0043] The right-angled valve 220 provided at the top of the valvemounting body 205 allows other accessories to be connected to the flowpath of the exhaust gases for leak testing, or other process diagnosticspurpose. For example, a leak detector unit or a residual gas analyzer(not shown) can be connected to the side port 222 of the right-angledvalve 220 for vacuum leak detection or for analyzing the exhaust gascomposition. The chamber close-off valve 210 has an inlet port 211 whichis connected to a process chamber (not shown) and an outlet port 212which is connected to a multi-stage trap 300 via a shut-off valve 391.

[0044] Two recessed openings 201, 202 are provided in the valve mountingbody 205 to accommodate a cartridge heater (not shown) and athermocouple temperature sensor (not shown). A thermally conductivepaste is used to line the inside of the opening to ensure good thermalcontact between the heater (not shown) and the valve body 205. Likewise,a thermocouple is inserted into the second opening 202, adjacent to theheater. Both the heater and the thermocouple control are connected aspart of a feedback circuit, similar to FIG. 1b, to a control unit foroverall control of the operation of the process chamber and the exhaustassembly 200. The unitary valve body design allows the use of a singleheater and thermocouple, which greatly simplifies the closed-looptemperature control procedure for the exhaust assembly 200. By usingdifferent heaters and thermocouple sensors, temperature control can beaccomplished over a wide range of temperatures for different processapplications. For example, in the case of TiN film deposition usingTiCl₄/NH₃ reaction, the exhaust assembly 200 is maintained at atemperature of about 150° C. The TiN film deposited on the interiorsurfaces of the exhaust assembly 200 is readily removed by a thermalchlorine-based cleaning process. However, after extended waferprocessing, a white powder deposit tends to accumulate inside theexhaust assembly 200. This powder deposit can easily be cleaned witheither water or hydrogen peroxide during periodic maintenance.

[0045] Multi-Stage Cold Trap

[0046]FIG. 3a and FIG. 3b respectively show an exploded perspective viewand a side view of the multi-stage cold trap 300 which comprises amulti-stage baffle structure 350 enclosed within a cold trap housing 360and a cold trap cover 368. An increase in the trapping efficiency ofcondensable by-products is achieved by increasing the collisions betweengas molecules and the various baffle plates which make up themulti-stage baffle structure 350. As illustrated in FIG. 3a, themulti-stage baffle structure 350 is cooled by circulating a heattransfer medium inside a cooling coil 399, which is welded onto thebaffle structure 350. The baffle structure 350 is attached to the coldtrap cover 368 by two mounting plates 396 using a plurality of screws394. The cooling coil inlet 399 i and outlet 399 o protrude through twoopenings 365 on the trap cover 368, with two viton O-rings 393 providingvacuum sealing against the trap cover 368 from the inside. Themulti-stage baffle structure 350 is secured inside the cold trap 300 bymounting the cold trap cover 368 onto the housing 360 with a pluralityof screws 398. Fourteen clearance holes 367 on the cold trap cover 368and corresponding threaded holes 366 around the perimeter 360P of thehousing 360 are provided for this purpose. A viton O-ring 397 providesvacuum sealing between the cold trap housing 360 and the cold trap cover368. As such, the cold trap 300 can be easily dismantled to facilitatecleaning during periodic maintenance.

[0047]FIG. 3b shows a side view of the various compartments, orchambers, 301 through 310 inside the cold trap 300. These compartments301-310 are typically defined by four surfaces, which may either beinterior walls (e.g., 360TW, 360FW) of the housing 360 or baffle platessuch as 361 or 362. The cold trap 300 can be visualized as divided intothree portions—top 300T, middle 300M, and bottom 300B. Exhaust gasesfrom the process chamber enter the top portion 300T of the cold trap 300via the inlet port 351. The top portion 300T comprises threecompartments 301, 302 and 303 separated by two vertical baffle plates361 and 362. The first compartment 301 can be considered an “entrance”compartment. It is defined by a front wall 360FW of the trap housing360, a top wall 360TW of the trap housing 360, a vertical baffle plate361 and a horizontal baffle plate 382. At this top portion 300T of thecold trap 300, the front wall 360FW of the housing 360 has an opening351 a (shown in phantom in FIG. 3b) at the inlet port 351 and serves asan entrance to the cold trap 300. An external heater 395 is disposedaround the exterior of the inlet port 351 of the cold trap 300 tomaintain a temperature of about 150° C. This helps minimize undesirabledeposits from forming within the inlet 351.

[0048] The first vertical baffle plate 361 extends from the top wall360TW to the bottom wall 360BW of the housing 360, while the secondbaffle plate 362 extends from the top wall 360TW to an intermediatedistance about ⅓ along the length of the housing 360. The first verticalplate 361 has three holes or apertures 361 a, 361 b, 361 c arranged asshown in FIG. 4a, which illustrates the view from the “front” of thecold trap 300. The inlet opening 351 a corresponding to the entrance ofthe trap 300 is shown in phantom to indicate its relative position withrespect to the three apertures 361 a, 361 b, 361 c in the first verticalbaffle plate 361. In this offset design, the apertures from eachapertured surfaces are located such that when the area of any apertureis projected along a direction perpendicular to the surface containingthat aperture, the “area of perpendicular projection” should preferablynot overlap or intersect any apertures on another apertured surfacedefining the same compartment. That is, the projected area correspondingto the inlet opening 351 a of the housing 360 should preferably notoverlap any of the apertures 361 a, 361 b, 361 c on the first verticalbaffle plate 361. Such an “offset” design increases the probability thatgas molecules exiting from the chamber valve 210 and entering the coldtrap 300 strike the first vertical baffle plate 361 prior to beingpumped through the openings or apertures 361 a, 361 b; 361 c of thefirst vertical baffle plate 361. Collisions of gas molecules with thecold baffle plate 361 cause molecules to lose kinetic energy, and allowstrapping of the molecules onto the front surface 361F of the baffleplate 361. Of course, some degree of overlap between different aperturesis not precluded from the present invention.

[0049]FIG. 4b shows the second vertical baffle plate 362 with twoapertures 362 a, 362 b arranged to be individually offset from the threeapertures 361 a, 361 b, 361 c of the first vertical baffle plate 361.The “areas of perpendicular projection” of the three apertures 361 a,361 b, 361 c of the first vertical plate 361 are shown in phantom. Thebaffle plate apertures used in the present invention are approximately 2in. (50.8 mm) in diameter. Dimensions cited in this embodiment are forillustrative purposes only, and other variations can also be usedwithout detracting from the spirit of the present invention. For optimaltrapping efficiency, the offset design should be used to position eachof the openings or apertures within the trap 300.

[0050] Returning to FIG. 3b, the middle portion 300M of the cold trap300 comprises three compartments 304, 305 and 306 respectively definedby the back wall 360BW of the housing 360, the first vertical plate 361and different combinations of two of the four horizontal plates 371,372, 373 and 374.

[0051] The first (top) and the last (bottom) horizontal plates 371, 374are identical in design, and extend across the entire width of the trapassembly housing 360. The second and third plates 372, 373 extend onlypartially across the housing 360—from the back 360BW to about ⅔ of thewidth, where it is brazed to the first vertical baffle plate 361.Although these plates can be screw-mounted to each other, brazing ispreferred because it ensures efficient thermal conduction among thecomponents of the cold trap 300. Similar to the vertical baffle plates361, 362 the horizontal plates 371-374 are also provided with apertureswhich are arranged to be offset from those in successive, or adjacentplates. A top view of the first horizontal baffle plate 371 is shown inFIG. 5a, with the aperture 372 a for the second horizontal baffle plate372 shown in phantom.

[0052] Another compartment 310 is defined by the horizontal plates 381,382, the first vertical baffle plate 361, and the front wall 360FW ofthe housing 360. This compartment 310 can be thought of as an “exit”compartment because it is connected to the exhaust assembly 100 via anopening 352 a in the housing wall 360FW through an outlet 352 and ashut-off valve 392. Exhaust gases that enter the multi-stage cold trap300 via the inlet valve 391 travel through the various compartments301-310 before exiting the cold trap 300 via the outlet 352.

[0053] As shown in FIGS. 3a and 3 b, a cooling coil 399 is welded orbrazed in a meander pattern to the vertical and horizontal baffle plates361, 362, 371, 372, 373, 374 starting from one side of the housing 360across to the other side, where a similar meander pattern is providedalong the baffle plates 361, 362, 371, 372, 373 and 374. This allows aheat transfer medium, such as cooling water, to travel from a coolantinlet 399 i adjacent to the bottom plate 374 to the top horizontalbaffle plate 371, along the direction shown by the arrows 3 in FIG. 3b.The heat transfer medium then continues across to the other side (notshown) of the housing 360, and exits from an outlet opening (not shown).In this embodiment, the cooling coil 399 is made of nickel-platedaluminum because of the need for compatibility with chlorine, which isused in a chamber clean process. Of course, other suitable materials mayalso be used, as long as they satisfy the requirements of good thermalconductivity and chemical compatibility with the exhaust and cleaningprocess gases. With an inlet water temperature around 20-25° C., thetemperature of the baffle plates can be maintained between 20-25° C.,while that of the trap body is between 45-70° C.

[0054] The bottom portion 300B of the cold trap 300 comprises threecompartments 307, 308, 309 which are separated by two vertical baffleplates 363, 361. These vertical baffle plates 363, 361 are designed andarranged in similar fashions as previously described for the plates 362,361 in the top portion 300T. That is, exhaust gas molecules undergosuccessive collisions with adjacent baffle plates as they travel fromone compartment to the next. With this multi-stage design, the cold trap300 offers a trapping efficiency approaching 95% for 2 μm sizeparticles.

[0055] All the baffle plates 361-363, 371-374, and the housing 360 inthe present invention are made of nickel-plated aluminum in order toensure chemical compatibility with chlorine, which is used in a chambercleaning process. Of course, depending on the specific processapplications, other materials such as stainless steel can also be usedas long as they have the requisite chemical compatibility and thermalproperties suitable for cold trap applications. Therefore, materialsused in this embodiment are meant to be illustrative only, and do notrepresent inherent limitations in the present invention.

[0056] Although the baffle plates 361-363, 371-374 of the presentinvention are arranged in vertical and horizontal directions, they areby no means the only possible arrangements. In fact, each of thecompartments 301-310 within the trap 300 may be defined by differentcombinations of baffle plates or interior walls of the housing 360. Forexample, a compartment 601 may be formed by only three surfaces asillustrated in a cross-sectional view of FIG. 6. Two of these surfacesmay be baffle plates 611, 612 each having at least one aperture 611 a,612 a and the third surface 613 may be disposed at an angle θ withrespect to the baffle plate 611. Gas molecules entering this compartment601 through the aperture 611 a of the baffle plate 611 collide with thethird surface 613. Some molecules will be adsorbed onto the surface 613while others will scatter off and further collide with baffle plates 611or 612. The location of the aperture 612 a should preferably be selectedsuch that molecules can exit via the aperture 612 a only after multiplecollisions with surfaces 611, 612 and 613. Therefore, the presentinvention encompasses design variations which seek to minimize theprobability of molecules passing through a trapping structure via adirect, non-collisional path; as well as those which seek to maximizethe collisions between exhaust gas molecules and cold surfaces.

[0057] Referring back to FIG. 3b, exhaust gases, after exiting thecompartment 309 of the cold trap 300, enter a particle filter 380, whichcomprises a bottom filter plate 381 with several slots 381 a, 381 b, 381c, 381 d (see FIG. 5c for a top view of plate 381) and a solid topfilter plate 382. Particles in the exhaust gases are trapped by afiltering material, such as a fine stainless steel gauze pad, placedbetween the bottom and the top filter plates 381 and 382, which iseffective for trapping particles with diameters above 2 μm. This filtermaterial is replaced during routine maintenance. In general, differenttypes of filtering materials can be selected to trap particles ofvarious sizes. Access to the particle filter 380 is provided by anaccess port 385 on the side 360S of the cold trap housing 360. (See FIG.3a.) A filter cover 388 is mounted over the access port 385 with aplurality of screws 384, and a viton O-ring 386 is used to providesealing between the filter cover 388 and the cold trap housing 360.

[0058] Shut-off Valves

[0059] Two custom-designed shut-off valves 391, 392 are provided at theinlet 351 and outlet 352 of the trap 300 for sealing the trap 300 fromthe exhaust assembly 200. This facilitates the periodic cleaningprocedure by allowing the cold trap 300 to be removed and transportedwith the trapped by-products safely contained therein. In the case ofthe TiN film deposition process, one of the reaction products ishydrogen chloride (HCl), which turns into hydrochloric acid uponexposure to moisture in the air. Therefore, the shut-off valves 391, 392allow a safe handling of the cold trap 300 during maintenance.Alternatively, for process applications which do not require cold trapcapability, the cold trap 300 can readily be isolated from the exhaustassembly 200 by closing the valves 391, 392.

[0060] The shut-off valve 391 has a very compact design, with athickness of only about 0.75 in. (19.1 mm). As such, it offers designflexibility and can readily be retrofitted to any existing chamber.While the current model is manually operated, it can easily be adaptedfor electronic control by adding a motorized or solenoid actuator tofacilitate movement of the valve. FIG. 7a shows an exploded view of theshut-off valve 391 (valve 392 is identical), which adopts a gate valvedesign, and FIG. 7b is a cross-sectional view of the assembled valve 391in its open position.

[0061] The valve 391 comprises a top plate 700, a gate 727, a bottomplate 740, and a handle 760. The gate 727, which is attached to thehandle 760 via two parallel shafts 721, 722, is a wedge-shaped platethat fits between the top plate 700 and the bottom plate 740. The valve391 can be open and closed by sliding the handle 760, and thus the gate727, along the direction indicated by the arrow 777.

[0062] As shown in FIG. 7a, the top plate 700 is substantiallyrectangular in shape and has an arcuate end 702 on one side and arectangular end 701 on the other. An opening 705, which serves as aninlet of the valve 391, is disposed slightly off-center away from therounded end 702. A small protruded portion 708 is provided around theperimeter of the top plate 700, while a recessed portion 709 is found onthe inside surface 707 of the top plate 700. Around the opening 705, theinside surface 707 is sloped (along the length indicated by A-B in FIG.7b) with respect to the outside surface 703, and a groove 708 isprovided around the opening 705 on the inside surface 707 to accommodatean O-ring 798.

[0063] The bottom plate 740 is also provided with an opening 745, whichserves as an outlet of the valve 391. The inside surface 747 of thebottom plate 740 has a protruded portion 749, which is also sloped(along the length indicated by C-D in FIG. 7b) with respect to theoutside surface 743 of the bottom plate. An O-ring groove 748 isdisposed around the opening 745 on the protruded portion 749 of theinside surface 747 to accommodate an O-ring 798.

[0064] When the valve 391 is assembled, the recessed portion 709 of thetop plate 700 interfits with the protruded portion 749 of the bottomplate 740, such that a space 755 is formed between the top and bottomplates 700 and 740 (see FIG. 7b). Viewed from the side (FIG. 7b), thespace 755 has a tapered cross-section between A-B and C-D, and has arectangular cross-section for the remaining portion of the space 755.The space 755 is large enough to accommodate the gate 727 and the shafts721, 722 to slide freely between the top plate 700 and the bottom plate740, along the direction of the arrow 777. When the valve 391 is closedby moving the gate 727 between openings 705 and 745, two O-rings 798located inside grooves 708, 748 provide sealing for the top plate 700and the bottom plate 740 against the gate 727. The protruded portion 708of the top plate 700 has another groove 776 to accommodate an O-ring 774for sealing between the top plate 700 and the bottom plate 740. The topand bottom plates 700, 740 are held together using a number of screws797 through clearance holes 786 in the top plate 700 and threaded holes785 in the bottom plate 740.

[0065] As shown in FIG. 7a, the gate 727 is screw-mounted onto the ends723, 724 of two cylindrical shafts 721, 722. The other ends 725, 726 ofthe shafts 721, 722 fit through two holes 715, 716 located at theprotruded portion 708 of the top plate 700. Two screws 795 fit throughtwo clearance holes 765 in the handle 760, and thread into the ends 725,726 of the shafts 721, 722. As such, the handle 760 is attached to thegate 727, and the gate 727 can be moved inside the space 755 of thevalve 391 along the direction of the arrow 777. The gate 727 iswedge-shaped, tapering towards the direction of the handle 760 (see FIG.7b). The taper of the gate 727 matches the sloped portions of the topplate 700 and the bottom plate 740 (indicated by A-B and C-D), andensures effective sealing against O-rings 798. This wedge-shape sealingsurface design is an important feature of the gate valve 391. Thereduced friction between the gate 727 and O-rings 798 allows the valve391 to be opened and closed with much less force than otherwisepossible, and also reduces wear on the O-rings 798 as they seal againstthe gate 727.

[0066]FIG. 7b shows the assembled valve 391 coupled to two KF flanges790 and 794 being held in place by clamps 791. An O-ring groove 706 isprovided around the opening 705 on the outside surface 703 of the topplate 700. An O-ring 796 seals against the flange 790, such as a KF-typeflange, which is welded to the valve body 200 of the exhaust assembly200. Similarly, a groove 746 on the outside surface 743 of the bottomplate 740 allows an O-ring 796 to seal against the flange 794. In thepresent embodiment, the KF flange 790 is welded to the valve body 200 ofthe exhaust assembly 200, while the other KF flange 794 is welded to thecold trap housing 360, and constitutes the inlet 351 of the cold trap300. A similar arrangement is used to couple another valve 392 betweenthe valve body 205 and the outlet of the cold trap 300. Each of these KFflanges 790, 794 is secured to the valve 391 by two flange clamps 791.FIG. 7a illustrates two flange clamps 791 attached to the outsidesurface 703 of the top plate 700 by wing-nut fasteners 792 and threadedstuds 704. The flange clamps 791 secure a KF flange 790 in place whenthe screws 793 are tightened, through clearance holes 788, intocorresponding threaded holes 787 on the outside surface 703 of the topplate 700. With screws 793 removed and fasteners 792 loosened, theclamps 791 can swing free of the KF flange 790, allowing the valves 391,392 and the cold trap 300 to be decoupled from the exhaust assembly 200as a self-contained sealed unit.

[0067] The valve 391 in this embodiment is made of nickel-platedaluminum to provide resistance to chlorine, which is used in a chambercleaning process, and all O-rings are made of viton. Of course, othermaterials can also be used (e.g., stainless steel for the valve), aslong as they are compatible with the chemicals and temperature used forthe specific process applications.

[0068] In the open position shown in FIG. 7b, the gate 727 is situatedtowards the rounded end 702 of the valve 391 and does not obstruct theopenings 705, 745, thereby allowing gases to pass through the valve 391.The shafts 721 and 722 are enclosed between the top plate 700 and thebottom plate 740. When the valve 391 is closed by pulling the handle 760out, the shafts 721, 722 protrude through the openings 715, 716 of thetop plate 700, and the valve 391 can be secured in its closed positionby inserting a pin (not shown) through the holes 775 (one of which isshown in FIG. 7b) of the shafts 721, 722. With both valves 391 and 392closed, the cold trap 300 can be isolated and decoupled from the KFflanges 790 of the exhaust assembly 200, and safely removed forcleaning.

[0069] Cold Trap Operation

[0070] During operation, exhaust gases enter the entry compartment 301of the cold trap 300 via the inlet 351. Some molecules are adsorbed whenthey collide with the front surface 361F of the vertical baffle plate361. Gases are then pumped through apertures 361 a, 361 b, 361 c of thefirst vertical baffle plate 361 into the adjacent compartment 302. Dueto the offset aperture design of the first and second vertical baffleplates 361, 362, most of the gas molecules entering the adjacentcompartment 302 collide with the front surface 362F of the secondvertical baffle plate 362, leading to additional adsorption ofcondensable molecules. As exhaust gases are pumped from one compartmentto the next, further adsorption occurs upon molecular collisions withcold surfaces of the baffle plates. This multi-stage collision processsignificantly enhances the adsorption efficiency of the cold trap 300compared to the commercially-available single-stage design. Finally,particles in the exhaust gas stream are trapped by the particle trap 380in the compartment 310 prior to exiting the cold trap 300.

[0071] Although two embodiments of the heated exhaust assembly 100, 200have been described with respect to their use in conjunction with aTiCl₄/NH₃-based TiN deposition chamber, it should be emphasized thatthey are generally adaptable to a variety of process chambers. In fact,any process which generates exhaust gases which either form deposits orcontain condensables may benefit from the use of this invention. Throughproper temperature control, one can confine the majority of deposits orcondensables to the cold trap 150, 300, and minimize such deposits onother parts of the exhaust assembly 100, 200. This is especiallyvaluable for processes in semiconductor fabrication, such as etching,deposition or implant, where highly corrosive or toxic gases are oftenpresent. Not only does the use of a temperature-controlled exhaustassembly prolong the life of vacuum system components, but it alsogreatly facilitates routine maintenance and provide a safe operatingenvironment.

[0072] Although various embodiments which incorporate the teachings ofthe present invention have been shown and described in detail herein,those skilled in the art can readily devise many other variedembodiments that still incorporate these teachings.

What is claimed is:
 1. An exhaust assembly for a semiconductorprocessing chamber comprising: a conduit for exhaust gases having atleast one heater and one temperature sensor attached thereto; and a coldtrap connected to said conduit comprising an inlet heated to a firsttemperature and a surface cooled to a second temperature.
 2. The exhaustassembly of claim 1 , wherein said exhaust assembly has a plurality ofheaters and temperature sensors connected to a closed-loop control unitto maintain said plurality of heaters at predetermined temperatures. 3.The exhaust assembly of claim 1 , wherein said cold trap furthercomprises a heater and a temperature sensor disposed around an inlet ofsaid cold trap and said heater and temperature sensor are connected to aclosed-loop control unit to maintain said inlet at a temperature withina range of about 150-200° C.
 4. The exhaust assembly of claim 1 ,wherein said conduit is maintained at a temperature within a range ofabout 150-200° C.
 5. The exhaust assembly of claim 1 , wherein said coldtrap comprises: a plurality of interconnecting chambers; and a coolingcoil abutting at least one wall of a chamber.
 6. The exhaust assembly ofclaim 1 , wherein said cold trap comprises a housing having an inletopening, an outlet opening, and a multi-stage adsorbing structuredisposed inside said housing between said inlet opening and said outletopening.
 7. The exhaust assembly of claim 6 , wherein said multi-stageadsorbing structure comprises: a plurality of baffle plates disposedinside said housing so as to form a plurality of compartments; and eachof said plurality of compartments is defined by a plurality of surfaceswherein a first surface has at least a first aperture defined thereinand a second surface has at least a second aperture defined therein. 8.The exhaust assembly of claim 7 , wherein each aperture of said surfacesdefining one of said compartments is disposed to be offset from each ofsaid apertures of other surfaces defining said one compartment.
 9. Theexhaust assembly of claim 6 , wherein said cold trap further comprises:a first valve connected to said housing at said inlet opening and asecond valve connected to said housing at said outlet opening; whereinsaid cold trap can be isolated from said conduit of said exhaustassembly by closing said first and second valves; and said isolated coldtrap, said first and second valves form a unitary sealed assemblyremovable from said conduit.
 10. An exhaust assembly for a semiconductorwafer processing system comprising: a unitary valve body; and amulti-stage trap assembly connected to said unitary valve body having atleast one isolating valve located between said unitary valve body andsaid trap assembly.
 11. The exhaust assembly of claim 10 , wherein saidexhaust assembly further comprises: a heater and a temperature sensordisposed in said unitary valve body; and a closed-loop control unitconnected to said heater and said temperature sensor to maintain saidconduit at a predetermined temperature.
 12. The exhaust assembly ofclaim 10 , wherein said multi-stage trap assembly comprises a housinghaving a first opening and a second opening, a multi-stage cold trap anda particle trap.
 13. An exhaust assembly for a semiconductor waferprocessing system, comprising: a unitary valve body; a multi-stage trapassembly connected to said unitary valve body having at least oneisolating valve located between said unitary valve body and said trapassembly, a housing having a first opening and a second opening, amulti-stage cold trap and a particle trap; said multi-stage cold trapfurther comprises a plurality of baffle plates cooled to a predeterminedtemperature, said plurality of baffle plates defining a plurality ofcompartments inside said housing; wherein said first housing openingprovides an entrance to a first compartment; said second housing openingprovides an exit out of a second compartment; and each one of saidremaining compartments is connected to at least two adjacentcompartments by apertures defined in two baffle plates.
 14. The exhaustassembly of claim 13 , wherein said plurality of baffle plates arecooled to said predetermined temperature by a cooling coil in physicalcontact with said baffle plates, and said predetermined temperature ismaintained by flowing a heat transfer medium through said cooling coil.15. The exhaust assembly of claim 13 , wherein each of said apertures ofbaffle plates defining adjacent compartments is disposed to be offsetfrom each other.
 16. The exhaust assembly of claim 10 , wherein saidmulti-stage trap assembly and said isolating valve are removable fromsaid unitary valve body as a unitary sealed assembly.
 17. The exhaustassembly of claim 16 , wherein said valve is a compact gate valvecomprising: a first plate having a first opening and an inside surfacewhich is sloped with respect to an outside surface of said first plate;a second plate having a second opening and an inside surface which issloped with respect to an outside surface of said second plate; awedge-shaped gate disposed between said first plate and said secondplate; wherein said wedge-shaped gate can be disposed in a sealingcontact position against both inside surfaces of said first and secondplate to isolate said first opening from said second opening.